Soil Formation and Development | Soil Science (Licensure Exam for Agriculturist)

Soil Formation and Development
Introduction
- Soil Formation: Breakdown of rocks through weathering.
Rocks and Minerals
- Definition of Rock: Solid mineral material forming Earth's surface.
- Types of Rocks:
- Igneous Rocks: Formed from molten magma (e.g., granite, basalt).
- Sedimentary Rocks: Accumulated rock fragments (e.g., limestone, shale).
- Metamorphic Rocks: Altered by heat and pressure (e.g., marble, slate).
- Minerals: Naturally occurring inorganic substances.
- Primary Minerals: Quartz, feldspar, mica.
- Secondary Minerals: Clay minerals, iron oxides.
Weathering Processes
- Physical Weathering: Breakdown without chemical changes.
- Examples: Freeze/thaw cycles, biological activity, exfoliation.
- Chemical Weathering: Chemical alteration of minerals.
- Examples: Hydrolysis, dissolution, oxidation.
Factors Influencing Soil Formation (CLORPT)
- Climate (C):
- Precipitation and temperature affect weathering and organic matter decomposition.
- Higher temperatures accelerate chemical reactions; cold climates enhance physical weathering.
- Organisms (O):
- Vegetation and soil organisms contribute organic matter and mix soil, enhancing fertility and structure.
- Relief/Topography (R):
- Shape and slope of land affect drainage, erosion, and sun exposure.
- Steeper slopes have thinner soils due to erosion; flatter areas accumulate more soil.
- Parent Material (P):
- Geological or organic precursors of soil determine initial properties.
- Inorganic (e.g., rocks) and organic materials (e.g., plant/animal remains).
- Time (T):
- Duration of soil formation affects soil maturity.
- Younger soils have less horizon development; older soils are more developed.
Soil Sequences
- Catenas: Soils differing primarily due to relief and drainage variations.
- Chronosequence: Soils differing due to the time elapsed since formation.
- Lithosequence: Soils differing due to variations in parent material.
- Climosequence: Soils differing due to changes in climate.
- Biosequence: Soils differing due to biological factors.
Basic Processes in Soil Formation
- Transformation: Chemical and physical changes of soil constituents.
- Translocation: Movement of materials within soil horizons.
- Additions: Inputs from external sources, such as organic material.
- Losses: Removal of materials from the soil system.